The present invention relates to a method and apparatus for producing a multifilament yarn from a heated thermoplastic melt.
DE-B 22 41 718 (Du Pont) and U.S. Pat. Nos. 3,771,307 and 3,772,872 disclose a method and apparatus of the described type which is characterized by the steps of melt spinning a yarn at a high withdrawal speed and then drawing the yarn, the drawing occurring along with a false twist texturing treatment.
It has been found that there exists a physical dependence between the withdrawal speed and the draw ratio that can still be realized thereafter. This interdependence occurs as a result of a partial orientation of the molecule chains that is realized by the high withdrawal speed which is in this instance more than 2,000 meters per minute. As a consequence, the elongation at break of the thus partially oriented yarn (POY) and, thus, likewise its subsequent stretchability are reduced. For a polyester yarn (polyethylene terephthalate, and others), and for a polyamide yarn (nylon 6 and nylon 6.6), the physical dependence may be noted essentially from the diagram of German Patent 22 54 998. "Normal withdrawal speed" and/or "normal draw ratio", as used hereafter, are meant to be a draw ratio, which maintains the relationships in accordance with this diagram, i.e., the partially oriented yarn is spun in conventional manner and not in accordance with the teaching of this invention.
Together with the total denier of the yarn that is to be produced, this physical dependence causes a limitation of productivity. The productivity again can be measured by the delivery or flow rate of the melt, i.e., the weight of the melt per unit time, expressed for example as grams per minute.
In a continuous spin-draw and takeup process, the increase in the withdrawal speed does not result in a corresponding increase in productivity, since as the withdrawal speed increases, the stretchability or draw ratio decreases and, consequently, the takeup speed changes only little or not at all.
In such a continuous spin-draw and takeup process, the yarn advances immediately after spinning to a draw zone, and is wound after passing through the draw zone.
In a discontinuous production process, a takeup occurs after spinning. The produced package is then supplied to a draw machine, and wound again after passing through the draw zone. In this process, the rate of flow, at which the melt is discharged, results from the total denier that must be reached at a given withdrawal speed and draw ratio. Due to the physical relationships, the conventional production process does not permit a significant increase in productivity to be realized for a yarn by melt spinning a partially oriented yarn and its subsequent drawing (see, treatise "Spinnstrecken-Schnellspinnen-Strecktexturieren" in International Textile Bulletin ITB, 1973, p. 373).
It is accordingly an object of the present invention to provide a method and apparatus for the production of a multifilament yarn which permits the production rate to be increased.